how to require all-or-none of a set of arguments using derive?

[dan-da]

I am trying to accept CLI args for optionally sending alert emails.

There are several options like admin_email, smtp_host, smtp_user, smtp_pass, etc.

The requirement is that if any of these are present then all must be present. But it is also ok for none to be present. (all-or-none).

Presently I have:

#[derive(Debug, clap::Parser, Clone)]
#[clap(name = "demo")]
pub struct Config {

    // other options omitted

    #[command(flatten)]
    pub alert: Option<Alert>,
}

#[derive(Debug, Clone, clap::Args)]
pub struct Alert {
    /// admin email for receiving alert emails
    #[arg(long, value_name = "email")]
    pub admin_email: String,

    /// smtp host for alert emails
    #[arg(long, value_name = "host")]
    pub smtp_host: String,

    /// smtp username for alert emails
    #[arg(long, value_name = "user")]
    pub smtp_user: String,

    /// smtp password for alert emails
    #[arg(long, value_name = "pass")]
    pub smtp_pass: String,

    /// sender email for alerts
    #[arg(long, value_name = "email")]
    pub smtp_from_email: String,
}

I thought that the alert: Option<Alert> might express the intention that its ok for none of the Alert fields to be present. But when I execute I still get an error that all the fields are required.

So how can I achieve the all-or-none requirement?

[dan-da]

Well, I was finally able to get something that works all-or-none. But it seems way too convoluted and verbose to be the best way to do this, so I'm still hoping for guidance.

Things to notice about this:

• required(false) + multiple(true) + requires_all() + args()
• group args are moved into Config, each as an Option<_>
• duplication of fields in Config and Alert. gross! smelly!
• added Config::alert() to generate an Option from optional fields. not necessary with initial approach. yuck!

I scoured docs, examples, discussions all day long and tried dozens of variations that did not work. This is the only one that did. I would suggest that all-or-none is an area ripe for documentation and/or api improvement.

#[derive(Debug, clap::Parser, Clone)]
#[clap(name = "demo")]
#[clap(group(
    clap::ArgGroup::new("value")
        .required(false)
        .multiple(true)
        .requires_all(&["admin_email", "smtp_host", "smtp_user", "smtp_pass", "smtp_from_email"])
        .args(&["admin_email", "smtp_host", "smtp_user", "smtp_pass", "smtp_from_email"])
))]
pub struct Config {

    // other options omitted

    /// admin email for receiving alert emails
    #[arg(long, value_name = "email")]
    pub admin_email: Option<String>,

    /// smtp host for alert emails
    #[arg(long, value_name = "host")]
    pub smtp_host: Option<String>,

    /// smtp username for alert emails
    #[arg(long, value_name = "user")]
    pub smtp_user: Option<String>,

    /// smtp password for alert emails
    #[arg(long, value_name = "pass")]
    pub smtp_pass: Option<String>,

    /// sender email for alerts
    #[arg(long, value_name = "email")]
    pub smtp_from_email: Option<String>,
}

#[derive(Debug, Clone)]
pub struct Alert {
    pub admin_email: String,
    pub smtp_host: String,
    pub smtp_user: String,
    pub smtp_pass: String,
    pub smtp_from_email: String,
}

impl Config {
    pub fn alert(&self) -> Option<Alert> {
        match (
            &self.admin_email,
            &self.smtp_host,
            &self.smtp_user,
            &self.smtp_pass,
            &self.smtp_from_email,
        ) {
            (
                Some(admin_email),
                Some(smtp_host),
                Some(smtp_user),
                Some(smtp_pass),
                Some(smtp_from_email),
            ) => Some(Alert {
                admin_email: admin_email.clone(),
                smtp_host: smtp_host.clone(),
                smtp_user: smtp_user.clone(),
                smtp_pass: smtp_pass.clone(),
                smtp_from_email: smtp_from_email.clone(),
            }),
            _ => None,
        }
    }
}